There have been a lot of other "firsts" in the 50 years of human spaceflight. Here's a look at some of the top milestones, from Gagarin's historic flight to humanity's first steps on the moon to the birth of space tourism.
The flight was a major milestone for humanity, and another victory for the Soviet Union in its escalating Cold War space race with the United States. In October 1957, the Soviets had stunned the U.S. by placing the first artificial satellite, Sputnik 1, in orbit around Earth.
Gagarin became a global celebrity after his return to terra firma. But he didn't live to see some of the other human spaceflight achievements his mission helped set in motion, such as humanity's first steps on the surface of the moon. Gagarin's plane crashed during a military training flight in March 1968, killing the cosmonaut at the age of 34.
Shepard's suborbital flight lasted only 15 minutes, carrying him to an altitude of 115 miles (185 km). He splashed down in the Atlantic Ocean just 302 miles (486 km) downrange of the Florida launch site. But the short trip marked the U.S.'s human spaceflight debut, laying the foundation for longer, more ambitious jaunts down the road.
The flight also showed that humans can pilot a vehicle during weightlessness and the rigors of re-entry. Shepard controlled many of the Freedom 7's movements, while Gagarin's flight was more automated.
The 26-year-old Tereshkova piloted the Vostok 6 vehicle, completing 48 orbits of Earth and staying in space for nearly three days. Upon landing, she became a national hero, like her countryman Yuri Gagarin.
The first American woman didn't reach space until two decades later, when Sally Ride flew aboard the space shuttle Challenger in 1983.
On March 18, 1965, cosmonaut Alexey Leonov made history's first spacewalk. He left the cozy environs of his Voskhod 2 spacecraft while in orbit around the Earth. Leonov stayed outside for 12 minutes, with only a spacesuit separating him from the frigid near-vacuum of space.
Leonov's suit ballooned greatly while he floated in space, complicating his re-entry to the Voskhod. Nonetheless, the spacewalk was a signficant achievement — one the United States matched less than three months later, when astronaut Edward White stepped outside his Gemini IV spacecraft.
NASA's Apollo 8 mission launched on Dec. 21, made 1 1/2 orbits of Earth, then lit out for the moon. As the craft left Earth in its rear-view mirror, astronauts pointed a television camera back at our planet. For the first time, humanity had a good look at Earth from afar, seeing it as a precious blue marble suspended in the black emptiness of space.
The mission arrived in lunar orbit on Dec. 24. On that date, the three Apollo crewmembers beamed home an iconic shot of Earth hanging in space with the desolate lunar surface in the foreground. They then delivered an unforgettable Christmas Eve message to a nation in need of healing — an America riven by the Vietnam War, racial inequality and other crises.
Chances are, they were glued to the TV. At 4:18 p.m. Eastern time on that date, the lunar module of NASA's Apollo 11 mission touched down on the surface of the moon. Shortly thereafter, Neil Armstrong's boot hit the lunar dirt, and the world heard perhaps the 20th century's most famous sentence: "That's one small step for man — one giant leap for mankind."
Humanity had set foot on another world for the first time ever. Armstrong and fellow astronaut Buzz Aldrin hopped around the lunar surface for more than 21 hours, collecting rocks, setting up experiments and planting an American flag (though they stopped short of claiming the moon for the United States). The world would never be the same.
NASA engineers determined that the oxygen in the Apollo capsule would run out before the craft could find its way back to Earth. But they figured out that the crew could use the attached lunar module — which was unaffected by the explosion — as a sort of lifeboat to survive the harrowing trip home.
The gambit worked, and the three astronauts splashed down safely in the South Pacific on April 17. The events — which were popularized in the award-winning 1995 film "Apollo 13" — prompted NASA to reconsider many aspects of its human spaceflight program, and they solidified in the public eye the space agency's reputation for problem-solving genius.
On July 15, NASA launched an Apollo spacecraft, which met up with a Soviet Soyuz in low-Earth orbit. In a mission known as the Apollo-Soyuz Test Project (ASTP), the two vehicles rendezvoused and docked, and their crews performed several experiments over the course of two days.
The mission tested the compatibility of rendezvous and docking systems for the two nations' spacecraft, and it laid the foundation for joint manned flights down the road. But the ASTP's main significance may have been symbolic, showing the easing of tensions between the U.S. and U.S.S.R.
The ASTP is sometimes unofficially called "Apollo 18," since it was the last of the Apollo missions. It was also the last U.S. manned space mission until the space shuttle's maiden flight in April 1981.
Salyut 1 was a far cry from today's huge, complex International Space Station. The structure was reported to be about 66 feet long and 13 feet across at its widest point (20 by 4 meters). The first cosmonauts attempted to board Salyut 1 on April 23, 1971, but docking problems prevented them from entering the craft. Another crew — flying aboard the Soyuz 11 spacecraft — finally made it inside on June 7 of that year.
The Soyuz 11 crew stayed onboard Salyut 1 until June 29, completing 362 orbits of Earth before heading back home. Tragically, all three cosmonauts died when their capsule unexpectedly de-pressurized during preparations for re-entry.
The first real space station didn't last long. On October 11, 1971, engineers fired Salyut 1's engines for the last time, bringing the structure lower and lower. The craft soon burned up in Earth's atmosphere over the Pacific Ocean.
When Columbia blasted off on April 12, 1981, it initiated the next phase of the United States' human spaceflight program. Over the next three decades, the various shuttles were workhorses, launching on a total of 133 missions. Two of these — Challenger's STS-51-L mission in 1986 and Columbia's STS-107 flight in 2003 — ended in tragedy, with the total loss of the shuttles and their crew.
Only two shuttle missions are left, as the shuttle program is slated to retire later this year. When that happens, NASA will begin concentrating on exploring asteroids and Mars — counting on the emerging private spaceflight industry to ferry astronauts to and from low-Earth orbit over the long haul.
It was a major milestone for the huge station, which is being assembled in low-Earth orbit by a coalition of space agencies from the United States, Russia, Canada, Japan and Europe. Construction began in November 1998 and is expected to be completed by 2012.
The $100 billion orbiting lab — which has about as much living space as a five-bedroom house — is the single most expensive structure ever built. NASA and the other space agencies are using the station to test exploration technology, perform a variety of experiments and gain knowledge that could help maintain crew health and performance in space.
Tito's trip was organized by the Virginia-based company Space Adventures, which has now sent seven tourists on a total of eight missions to the ISS. Some of them have reportedly paid up to $35 million for the journey. The last flight was in 2009, but an increase in Soyuz production is allowing the company to sell seats again, for trips starting in 2013.
Tito's journey showed that spaceflight could be open to regular people. OK, not regular people — super-wealthy people. But the cost of space tourism jaunts should come down significantly as private spaceflight ramps up. Virgin Galactic, for example, is selling seats for subortibal joyrides for $200,000, with the first passenger flights possibly occurring by 2012.
On Oct. 15 of that year, China launched spaceflyer Yang Liwei into space in the Chinese-made Shenzhou 5 vehicle, which was carried aloft by a Chinese rocket. The nation has continued to develop its human-spaceflight program since then, launching two more manned missions. And in September 2008, a Chinese "taikonaut" made the nation's first-ever spacewalk.
With this accomplishment, the SpaceShipOne team — led by famed aerospace engineer Burt Rutan, chief of the firm Scaled Composites — won the prestigious $10 million Ansari X prize. The back-to-back flights also showed that human spaceflight will not be the exclusive province of government agencies, or government-designed vehicles, for too much longer.
The SpaceShipOne design eventually morphed into SpaceShipTwo, which became the basis for Virgin Galactic's VSS Enterprise vehicle. The Enterprise could start carrying paying customers on suborbital joyrides as early as 2012, at $200,000 per seat.
With the flight, SpaceX became the first private company ever to launch a spacecraft to Earth orbit, then recover it after re-entry. Previously, only six nations or governmental agencies had accomplished the feat.
Dragon's first flight was just a test — preparation for NASA-funded supply runs to the International Space Station. But Dragon's success bodes well for private human spaceflight; SpaceX has already submitted a proposal to NASA to upgrade Dragon to a crew-carrying craft.
Dragon won't be shuttling astronauts around in the next few months, however. The spacecraft will make at least 11 more flights — and the Falcon 9 will launch at least 17 more times — before the company is ready for manned missions, SpaceX officials have said.